Decorating: Sanding and Power Sanding
Drills with attachments or purpose-made tools, used with abrasive papers or metal discs, can be used to rub down surfaces. Preparing a surface can be a long job; but much of the tedium is removed by using power equipment.
These are self-contained units with a flat, elongated cushion-backed abrading surface, which rotate in small circles over the work area. Abrasive paper is stretched over the flat cushioned pad and held in place by pressure clips.
This type of sander is best used for light finishing work, such as rubbing down or keying paintwork, for further paint coats. Orbital sanders may be in the form of power-drill attachments or integrated tools.
In use, the weight of the tool will give sufficient pressure but hand guidance will be needed to prevent the pad from sliding about on the surface.
The power tools more often used for heavier work are rubber or flexible-foam discs and drum sanders.
A rubber disc attachment consists of a flexible rubber backing pad to which are attached discs of abrasive paper. These are secured by means of a centre locknut and plate, or fixed with a special.
The rotary action of a fixed sanding disc may leave unsightly, scored, circular markings on the surface. The flexible type, with a knuckle joint or foam back, produces generally better work.
When using the fixed rubber disc, do not use the entire surface of the disc at one time; work with the disc tilted at an angle of 30° – this will help to minimize swirl marks.
Do not exert heavy pressure, as this may overload the drill; use light sweeping strokes. Start with a coarse paper, working through to finer paper and, for a very fine surface, use a hand-held sander to finish off.
Ais not generally suitable for removing paint. The friction set up between the paper and the surface generates enough heat to melt the paint which is then driven into the surface and also clogs the paper.
Bare wood is best sanded with the grain but when using a disc sander this is not possible.
A, which is a foam rubber wheel with an outer-covering, or tyre, of abrasive paper will sand along the grain. It can be used on flat, convex or concave surfaces.
The abrasive paper is held in place with non-hardening. Where adhesive fails before the paper is worn, apply more adhesive to the non-abrasive surface.
To fix an abrasive paper on to a disc with a non-hardening adhesive, rotate the backing disc, spreading the adhesive while running the drill.
Stop it and then press the abrasive disc into place; between changing the discs remove any adhering adhesive by rotating the backing disc and, at the same time, skim off the adhesive with a blunt piece of metal held against the moving disc.
Wire-brush attachments, either in the form of a cup or a disc, fixed by a centre spindle into the chuck of a, can be used to prepare rusted surfaces.
The choice of attachment depends on the form of the surface; a section of guttering, for example, may best be treated with the cup attachment; the inside of metal guttering may more easily be cleaned with the disc attachment, which operates end on.
Take care not to damage the surface, as a wire brush is fairly harsh in operation. It is also advisable to wear protective gloves and goggles as a guard against flying particles of rust.
The finish on sanding papers depends on the number of abrasive particles, or granules, to the mm2. This is called the ‘grit’. The larger the number of grits, the finer the paper.
Papers range from coarse to fine. You will only achieve a satisfactory finish if the correct paper is used. However hard you rub with a coarse paper you will not obtain a fine finish.
Start work with a coarse paper and work through the range to fine.
It is not possible successfully to rub down damp wood. Abrasive paper should always be stored in a dry place as once it is wet it is useless.
There is, in fact, now no such thing as sandpaper; the abrasive quality of various types of paper is achieved by other forms of surface coating.
These may be granules of glass, emery, garnet, silicone-carbide or flint. Glass-paper is the most common.
Each type of surface is used for different finishing jobs and can be used either with a hand-held block, a power tool sander or attachment to a power tool.
Glass or garnet paper
These are used for obtaining a fine surface finish on bare wood. Garnet paper is harder wearing, and, therefore, lasts longer and gives a cleaner cut.
Is more commonly known as ‘wet and dry’. It is used wet to prepare painted wood or metal surfaces. When used wet, silicone-carbide paper tends to leave a muddy deposit on the surface being prepared. This should be wiped off periodically to avoid clogging the paper. Wet paper gives a smooth finish. It is used dry for exactly the same purpose as garnet or glass paper.
Emery paper is used solely for preparing metal surfaces.
Tungsten carbide discs and pads can be attached to disc or orbital sanders. These have the advantage of a very long life and do not easily clog.
10. November 2011 by admin
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